Conventionally, for scanning several paper sheets, the paper sheets should be manually placed on a scanning platform of the image scanner one by one. This means of manually feeding the paper sheets is time-consuming and laboring. Nowadays, the image scanner usually has a document feeder for successively and continuously feeding many paper sheets. As known, a conventional document feeder has a sheet pick-up module arranged in the sheet feeding channel for automatically feeding the paper sheets one by one at a time.
When the paper sheets are placed on the sheet feeding channel to be scanned, the front edges are usually inserted into the sheet feeding channel and thus several paper sheets may be simultaneously fed by the sheet pick-up module. For assuring that a stack of paper sheets are precisely positioned within the sheet feeding channel, the document feeder further has a stopper under or above the sheet pick-up module. When the stack of paper sheets enters the sheet feeding channel, the stopper is sustained against the front edges of the stack such that the paper sheets are positioned under the sheet pick-up module. Once the paper sheets are stopped by the stopper, the user may feel that the paper sheets are placed in position. When the sheet pick-up module performs the sheet pick-up operation, the stopper is shifted such that the paper sheets are smoothly transported through the sheet feeding channel.
FIG. 1A is a schematic perspective view illustrating the sheet pick-up module and the stopper of a conventional document feeder. This document feeder is for example disclosed in U.S. Pat. No. 6,792,241, and the contents of which are hereby incorporated by reference. The stopper 12 is pivotal and disposed under the sheet pick-up module 11. The sheet pick-up module 11 comprises a sustaining portion 111. Correspondingly, the stopper 12 comprises a tilt portion 121 and a sheet stop portion 122. When the sheet pick-up module 11 is lifted to a standby position, the sheet stop portion 122 is rotated to an upright position so as to be sustained against the front edges of the stack of paper sheets. Whereas, during the sheet pick-up module 11 is lowered to a sheet pick-up position, the sustaining portion 111 is also lowered down to touch the tilt portion 121 of the stopper 12. In response to the external force generated from rotation of the sheet pick-up module 11, the sheet stop portion 122 is rotated under the sheet feeding channel. Under this circumstance, the paper sheets can be smoothly transported through the sheet feeding channel without being stopped by the stopper 12.
Please refer to FIG. 1B, which is a schematic cross-section view illustrating relative locations of the sheet pick-up module and the stopper of the conventional document feeder. However, the stopper 12 of the conventional document feeder still has some drawbacks. For example, when a stack of paper sheets are positioned within the sheet feeding channel, if the an external force exerted on the paper sheets is very large or if the front edges of these paper sheets are not aligned with each other, the top paper sheets St may suppress the tilt portion 121 of the stopper 12. Under this circumstance, the sheet stop portion 122 is rotated under the sheet feeding channel before the sheet pick-up operation is done, so that the function of the stopping the paper sheets is lost.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop an improved document feeder according to the present invention through wholehearted experience and research.